Due to the shunting of oxygen-poor and carbon dioxide-rich blood into the systemic circulation, a compensatory hyperventilation resulting in an appropriate alveolar and pulmonary venous hypocapnia did occur. Since shunt volume does increase with progressive exercise in Eisenmenger syndrome, alveolar hyperventilation increases proportionally to shunt volume in order to maintain a normal PaC02, whereas Pa02 cannot be improved by hyperventilation in central cardiac right-to-left shunt. Considering the stable PaC02 at maximal exercise performance, an increasing hypoxic contribution to ventilatory control appears unlikely. other
It should be emphasized that the interpretation of our findings is based on noninvasive measurements. Therefore, some of the conclusions are based on assumptions with respect to exercise physiology in these complex lesions.

Clinically, it is a clear advantage of CPX being a well-tolerated and noninvasive but accurate tool for the evaluation of functional capacity. In the presence of such complex pathophysiologic states as cyanotic congenital heart disease, it certainly would be helpful to supplement these measurements with simultaneously obtained invasive hemodynamic and metabolic data. However, we think that such an invasive approach is hard to justify in this patient population.Conclusion
In cyanotic patients with congenital heart disease, CPX with gas exchange analysis provides additional and independent information, permitting more accurate and objective evaluation of their symptomatic state. In our patients, cyanosis and VE alone did not accurately reflect the symptomatic state. Peak V02 did partially correlate with it, but was not able to describe the entire spectrum of symptoms as judged by the ability index and NYHA class.
Overall, the summation of disease-related factors is important for the determination of symptomatology in these patients. These complex alterations were reliably integrated by the ventilatory efficiency at rest and under exercise. Due to the fact that the AT could not be determined by the analysis of gas exchange kinetics in a number of cases, this established, motivation-independent parameter should carefully be interpreted in the assessment of symptoms in this group of patients.